Colloidal properties of aqueous dispersions of ultradispersed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> prepared by explosion synthesis

The electrosurface properties of aluminum oxide particles prepared by shock—wave loading of aluminum powder in an oxygen-containing atmosphere and the aggregation stability of its aqueous dispersions are studied by the macroelectrophoresis method, potentiometric titration, and photometry. The enhanced stability of the dispersions in acid media and in the vicinity of the isoelectric point compared to that in alkaline media is explained by the effect of the structural component of the disjoining pressure, which appears due to the predominant hydration of the cationic forms of aluminum that are present on the surface of dispersed phase particles.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 128–131. Original Russian Text Copyright © 2005 by Chiganova, Nafikova.     

Influence of metal-containing lubricants on characteristics of polyvinyl chloride

The influence of metal-containing lubricants based on monoesters of glycerol and higher isomeric saturated monocarboxylic acids on characteristics of polyvinyl chloride was studied.     

Application of the united atom model for estimating the lifetime of negative molecular ions relative to electron autodetachment

A model proposed for describing the scattering of low-energy electrons (whose energy ranges between thermal energy and several electronvolts) from polyatomic molecules makes it possible to estimate the lifetime of shape resonances. The parameters of the model are determined by specific structural and experimental characteristics of molecules. The results of approximate computations of the lifetimes for negative ions of molecules with different symmetries (diatomic halogens, parabenzoquinone, fullerene C₆₀, benzothiadiazoles, anthraquinone derivatives, and substituted benzene forms) are presented. The obtained data show that the lifetimes are sufficient for the formation of fragment ions observed in the mass spectra of negative ions.     

Dissociative electron attachment in selected haloalkanes

Three mono-substituted and six poly-substituted haloalkanes derivatives were investigated by means of negative ion mass spectrometry (NIMS). Available electron transmission spectroscopy (ETS) data were used for the treatment of NIMS results. Comparison of the ETS spectra of mono-substituted bromo- and chloroalkanes show that these families of compounds exhibit similar regularities in the process of NI formation. Capture of the p-partial wave dominates in the lowest anion state formation. In the series of mono-substituted bromo- and chloroalkanes the energy difference (Shift) between the vertical attachment energy (VAE) in ETS spectra and the maximum of the NI formation in dissociative electron attachment (DEA) spectra correlates approximately linearly with the VAE value for the given molecule. The slopes of these dependencies are different for the mono-substituted chloro and bromo derivatives. It is conjectured that, in the derivatives di-substituted in the 1,2-positions, there is a shallow minimum in the repulsive anion potential curve, which makes possible temporary trapping of the anion. This delay is long enough for the rearrangement process and formation of the Hal2- ions. This effect is not detected in 1,1-halogenated derivatives.     

Intramolecular interactions in acyclic and macrocyclic compounds containing nucleotide bases

Acyclic and cyclic counterparts containing thymine and two 3,6-dimethyluracil fragments bridged by methylene chains have been prepared and studied by UV and NMR spectroscopy; in water the uracil units of the acyclic counterpart form an intramolecular stack but arrange in a linear array in chloroform while the fragments of the uracilophane form an intramolecular stack both in chloroform and water; uracil units of bis(3,6-dimethyluracil-1-yl)butane and the macrocyclic counterpart form a stack in chloroform.     

Violation of frozen shell approximation in dissociative electron capture by halogenated anthraquinones

A series of halogenated anthraquinone (AQ) derivatives has been studied by means of electron capture negative ion (NI) mass spectrometry (ECNI-MS). 1Cl-AQ and 2Br-AQ display dramatically steep positive temperature dependencies of Hal(-) ion abundance in the low electron energy region. Molecular NI intensity decreases rapidly with increasing temperature in the case of 1I-AQ. In the case of 2Br-AQ, a metastable NI peak (m/z 22.9) corresponding to the process BrAQ(-) --> Br(-) + AQ(0) was recorded. This means that the characteristic dissociation lifetime of the molecular NI Br-AQ(-) is at least approximately 25 micros at the energy approximately 0.67 eV in the low-temperature spectrum (T approximately 80 degrees C), and at the energy approximately 0.13 eV in the hot spectrum (T approximately 290 degrees C). Together with the observed temperature dependence of the 2Br-AQ curves of effective yield (CEY), this proves that this anion dissociates according to Coulson's model. The same halogen anion behavior is observed in the case of 1Cl-AQ. There are three consecutive stages in the process of molecular NI dissociation of Cl- and Br-substituted AQ, namely, electron capture into the empty pi-orbital by means of the shape resonance mechanism, followed by a radiationless transition into the ground electronic pi-state of the anion, as predicted by Compton in the case of the parabenzoquinone molecule, and, finally, a fluctuative dissociation of the molecular NI accompanied by the transition from the pi-term into the sigma-term, so-called predissociation. Calculations show reasonable agreement with the experimental data. In the case of 1I-AQ, an effect of inversion of empty levels in the process of electron capture by the molecule takes place, a violation of the so-called frozen shell approximation. The phenomenon found may be of significance not only in the case of ECNI-MS, but also in other experimental investigations using low-energy electron-molecule and ion-molecule collisions.     

Modification of fullerene C60 by phosphorylated diazo compounds

New representatives of phosphorylated methanofullerenes were prepared by the reactions of [60]fullerene with O,O-diethyl -diazoethyl- and O,O-diethyl -diazobenzylphosphonates. Electrochemical reduction of the above-mentioned products proceeded stepwise and reversibly.     

Phosphorylation of Pyrimidinophane in the Reversed Micellar Solutions of Cationic and Nonionogenic Surfactants

Reactions of a macrocycle containing three pyrimidine fragments and N,N′-bis(2-methylthio-6-methylpyrimidin-4-yl)-hexamethylenediamine with p-nitrophenyl bis(chloromethyl)phosphinate in the micellar solutions of cetyltrimethylammonium bromide, polyethyleneglycol-600 laurate and their mixture in chloroform was investigated spectrophotometrically. Catalytic activity of micelles depends on their structure, concentration of surfactants, molar fraction of the latter in solution, and structure of the nucleophilic reagent.     

Reactions of pyrimidinophanes and their acyclic analogs with electron-deficient substrates

Acyclic and macrocyclic compounds having different numbers of pyrimidine fragments and nitrogen atoms in the polymethylene bridges or in substituents at the pyrimidine rings reacted with 2,3,5,6-tetrachloro-1,4-benzoquinone and 1,4-benzoquinone according to the charge transfer scheme to give products with an ionic structure. The reaction was accompanied by protonation of nitrogen atoms in the polymethylene bridges or in substiuents at the pyrimidine rings and reduction of 2,3,5,6-tetrachloro-1,4-benzoquinone or 1,4-benzoquinone to 2,3,5,6-tetrachlorobenzene-1,4-diol or benzene-1,4-diol, respectively. The isolated products are dielectrics.